The invention concerns an apparatus for applying at least one surface portion of a transfer layer of a transfer film to a web of material, wherein the apparatus has at least one support roller and at least one pressure roller for pressing the web of material and the transfer film against the at least one support roller, wherein the at least one pressure roller is resiliently supported by means of at least one resilient arrangement and wherein the apparatus has at least one adjusting device for varying a spring rate of the at least one resilient arrangement and thus for varying a pressure contact force of the at least one pressure roller against the at least one support roller. The invention further concerns the use of such an apparatus.
Differing pressure contact forces of pressure rollers against a support roller lead to differing adhesion of a transfer layer to the web of material and should therefore be avoided as far as possible. Plate springs have therefore already been used as an elastically resilient arrangement for such apparatuses, which plate springs have a strong damping action and, in each spring stroke movement, produce a differing pressure contact force in respect of the pressure roller against the support roller. It is therefore not possible to achieve reproducibility of the pressure contact force of a pressure roller against the support roller, with plate springs. Accordingly elastic coil springs have been used as the resilient arrangement for apparatuses of that kind, which in each spring stroke movement produce an identical pressure contact force for the pressure roller against the support roller. A respective coil spring is provided for each pressure roller, the respective coil spring being arranged adjacent the respective pressure roller and having to be individually adjusted by hand. For that purpose it is necessary for the machine in which the apparatus is fitted to be completely stopped.
The basic structure of a machine suitable for that purpose is to be found in DE 32 10 551 A1, in which it is possible to find an apparatus having a heated embossing or support roller and a group of pairs of pressure rollers. In that case a flexible web of material is drawn off a supply roll and brought together with an embossing or transfer film which is made up of a carrier or backing film and the transfer layer, over direction-changing rollers, and conveyed through a gap between the support roller and the pressure rollers. The pressure rollers are pressed against the transfer film, the web of material and the support roller by way of adjusting cylinders so as to provide the required pressure for transfer of the transfer layer of the transfer film on to the web of material. In that arrangement the pressure rollers are disposed in such a way that the web of material and the transfer film pass around the support roller over about 170° and a so-called roller cage is formed. After leaving the support roller the web of material which is provided with the transfer layer in region-wise manner or over its full surface area is separated from the carrier film and possibly non-transferred regions of the transfer layer. The pairs of pressure rollers are mounted on rocker arms which are in turn respectively tiltably mounted on angle levers. The angle levers are each tiltable about a respective axis which is parallel to the axis of rotation of the support roller.
In that case at the present time the width of the pressure rollers does not correspond to the entire width of the support roller but individually supported pairs of pressure rollers are usual for each trace or line to be transferred. In order to compensate for the deflection which occurs in that situation in respect of the carriers for the pressure rollers along the longitudinal axis of the support roller, a resilient mounting arrangement was provided for the pressure rollers by way of the coil springs.
When changing the web of material and/or the transfer film it is necessary for the pressure contact force of each pressure roller or each pair of pressure rollers against the support roller to be freshly adjusted. To do that the entire machine has to be stopped and the roller cage has to be pulled out from under the support roller. The coil spring of each individual pressure roller is adjusted by hand, the machine is re-started and the result is checked. Optimising the pressure contact force of the pressure rollers is thus extremely time-consuming and often takes days. In most cases the optimisation procedure is therefore already broken off prior to reaching the optimum in order to keep the amount of time involved and the material consumption within limits. Furthermore the use of coil springs suffers from the disadvantage that they are sensitive to corrosion and have to be replaced at regular intervals. Thus for example vapors which escape from the web of material or the transfer film have an adverse effect on the coil springs. As a consequence of the maintenance operations that makes renewed optimisation of the pressure contact forces necessary even without a change in the web of material or the transfer film.